Interferometer seeker



1965 R. KENT ETAL 3,202,992

INTERFEROMETER SEEKER Filed May 28. 1962 3 Sheets-Sheet 2 FIG. 2

/TRANSVERSE AXIS THROUGH x CENTER OF ARRAY HEADING OF MISSILE ANTENNA ELEMENTS 2 /0 a n l/ +j 6+1? FIG. 3 d a d [3 /2 LOCAL +1 4 014 OSCILLATOR s S a V DELAY LINE 1 AXIS 0F ARRA I REFLECTION SIGNAL 5- OFF OF TARGET I \vAvE FRONT FIG. 4

l] AXIS OF ARRAY 3 Aug. 24, 1965 KENT ETAL 3,202,992

INTERFEROMETER SEEKER Filed May 28. 1962 3 Sheets-Sheet 3 I; 1 1 v. 1 LLZI LZI l7 l l8 /6 PATTERN FORMING NETWORK FDIFFERENGE sum PATTERN PATTERN FIG. 5

DIFFERENCE PATTERN VVVV U U VVAVAV'G SUM PATTERN United States Patent 3,202,992 INTERFERUMETER SEEKER Robert L. Kent, Andover, and Joseph C. Nowell, Cambridge, Mass., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed May 28, 1962, Ser. No. 199,229 7 Claims. (Cl. 343-100) The present invention relates to a missile homing system and more particularly to an electronically scanned interferometer seeker for providing electrical signals indicative of the true rate of change of the lead angle from a missile to a target.

An object of the present invention is to provide increased received signal strength thereby increasing maximum range and accuracy thereof for target detection and initial lock-on.

Another object of the present invention is to provide a semi-active terminal guidance system of improved angular resolution resulting in better missile performance in the presence of clutter, multiple targets, and noise jamming.

A further object of the present invention is to provide an interferometer seeker for the direct measurement of the target lead angle in the pitch and yaw planes of the missile permitting a correction for the variation in angular rate sensitivity with the target lead angle.

Another object of the present invention is to provide an interferometer seeker for indicating the rate of change of lead angle to a target.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description whenconsidered in connection with the accompanying drawings wherein:

FIG. 1 is a schematic block diagram of the present invention;

FIGS. 2, 3, 4, and 6 are explanatory diagrams to aid in the understanding of the present invention; and

FIG. is a schematic diagram of one embodiment of a pattern forming network. 7

Referring more particularly to the drawings, FIG. 1 shows a block diagram of an interferometer seeker for use in a ram-jet'missile to provide semi-active terminal guidance. The outer shell 8 of the missile, shown in cross section in FIG. 1, is approximately 10 wavelengths in diameter (about inches at C-band). Antennas are grouped in four arrays 1, 2, 3, and 4 of seven elements 10, each around the periphery of the outer shell as far forward as possible. The axes of arrays l and 3 are vertical and perpendicular to a longitudinal axis of the missile at the middle receiving element 11 with the receiving fan beam scanning a i30 sector in the pitch plane of the missile with the bandwidth of approximately 13. Similarly, the axes of arrays 2 and 4 are transverse and perpendicular at the middle receiving element 11 to a longitudinal axis along the missile shell with the fan beam receiving pattern for each array 2 and 4 being scanned in the yaw plane of the missile. Each pair of spaced arrays have a receiving channel to detect and measure the received reflected signals off a target.

For the comprehension of the present invention, certain basic relationships between the missile and a target and between the receiving beam of the antenna arrays and the pitch and yaw planes of the missile need to be defined. From FIG. 2, the coordinate system through array 3 is illustrated. X is the transverse axis through the center of array 3 perpendicular to the linear axis Z of the array. The heading of the missile is considered to be along a longitudinal axis through the center of the array perpendicular to X and Z. The bearing or lead 3,202,992 Patented Aug. 24, 1965 ice angle between the missile and the target is defined as 3 measured from the heading direction or the Y axis of the missile to the line of sight to the target T. The pitch and yaw angles from the missile to the target are represented by qi and 6. These angles are the projection of the lead angle 5 in the pitch and yaw planes of the missile respectively.

It is known that a transmitting antenna will radiate a beam broadside, that is, normal to the axis of a linear array when the seven elements of the array are excited in phase. Likewise, an antenna of a linear array of elements when receiving will have its receiving beam broadside to the linear axis of the array when the receiving signals at the elements 10 are in phase. However, FIG. 3, for example, shows a receiving array of seven elements 10 spaced an equal distance d apart receiving a signal at an angle a from the broadside position of a receiving beam. For the elements to be excited together and the reception maximized, the phase difference of the electrical signals on the seven elements must be such that the received signal on elements of the left of center element 11 must progressively lead by the same amount that signal received at the elements on the right. When the received signals are at an angle to the broadside position of the receiving beam, the phase of the excitation on any element can be represented by a complex function 6". In this expression, 1/ is the electrical phase difference between adjacent elements. With the center element 11 taken as a reference point for the received signal, the represented function of the phase of the signal on elements 10 to the left of the center element 11 becomes progressively e+ and 6 and to the right 6- and ej With the received signals on the elements in phase, the beam angle would be zero degrees or broadside to the linear array.

If n is considered to be the space time delay or the space phase between waves of receiving signals then from FIG. 3, it can be readily derived that n=d sin a f where d is the distance between the elements 10. From the preceding description, the electrical phase diiference 1,0 of the received signal between the element on the in radians, then n must be measured in radians. Theres along the delay line.

fore, with d measured in radians and substituting 1,1/ for n in Equation 1,

Thus if the electrical phase difference between the elements of a receiving antenna of linear array can be determined, then the receiving beam angle a can likewise be determined from Equation 2. With reference to the missile coordinate system of FIG. 2, the beam angle a for array 3 is the same as pitch angle d) and for array 2 it is the same as yaw angle 6.

The phase-scan technique of the present invention is accomplished by phasing local oscillator signals rather than the received signals. In order to establish the appropriate phase shifts on the local oscillator signals for mixing with the received signals for forming a receiving beam, the local oscillator signal is fed to one end of a delay line 14 having output taps 15 at a uniform spacing The delay line is designed so that the spacing s between the output taps 15 of the delay line is an integral number of wavelengths at the center frequency of the local oscillator signal and consequently the output signals from the taps are in phase. At frequencies removed from the center frequency, an integral number of wavelengths no longer exist between the taps, resulting in a progressive phase variation along the delay line. The amount of phase variation can be controlled by changing frequency of the local oscillator attached to the delay line, thus frequency scanning of an array in one dimension is accomplished.

The relationship of a received reflected signal off a target between two separated linear arrays 1 and 3 is illustrated in FIG. 4. The distance between arrays across the missile is designated k. It is evident that if the target signal is received along the missile heading, the receiving arrays would be excited in phase. However, as it is shown in FIG. 4, the signals are received at an angle measured from the direction of missile heading or the Y axis to a line-of-sight to the target. This angle projected in the XY plane defined by the coordinate system of FIG. 2 and shown in FIG. 4 has been defined as u. The space time delay between the signal received at arrays 1 and 3 is q. From FIG. 4, it is apparent that q=k sin u Angle u as defined from FIG. 4 for antenna arrays 1 and 3 is the same as the yaw angle with respect to the missile coordinate system of FIG. 2. For arrays 2 and 4 the angle u would then be the same as pitch angle Referring to the schematic diagram of FIG. 1, the signals received on each of elements of array 3 are fed to a balanced crystal mixer 12 for each element respectively. These received signals on the elements 10 of any array have the same linear phase difference therebetween since the array elements are uniformly spaced apart along the axis of the array. The linear phase difference between the elements depends upon the angle that the receiving signals are being received in comparison with a beam direction normal to the axis of the antenna array. Considering the middle element of array 3 as the phase center thereof, as shown in FIG. 3, the signals received on the elements to one side of the middle element will have opposite phases respectively from signals received on the other side. With the middle element 11 as a reference point, the element nearest to it will have a received signal with a certain phase dilference from the signal received at the middle element. The received signal on the next element in array will have the same phase difierence from the signal received on the adjoining element so that there is a progressively increasing integral number of phase difierences of the signals received along the array.

The klystron local oscillator 13 is connected to a RF deay line 14 which has output taps 15 equally spaced along the line so that the phase shift of the local oscillator signal is the same between adjoining taps of the line. Local oscillator excitation is fed from the equally spaced taps 15 of the delay line 14 to each of the mixers 12 respectively. A difference frequency signal between the received signal at each element 10 of the antenna array and the local oscillator signal from a corresponding tap 15 of the delay line 14 is selected at each mixer 12 to give a mixer output signal at an intermediate frequency.

The intermediate frequency output signal of each mixer 12 is applied to a pattern forming network 16 wherein sum and difference pattern output signals are obtained. The pattern forming network 16 shown schematically in FIG. 5 illustrates the manner of adding separately the signals from the mixers associated with one part of the antenna array and from the mixers associated with the other part of the antenna array in summers 17 and 18 and then subtracted from each other in a coaxial hybrid ring 19 to form a difference pattern output. The signal from the middle mixer associated with the middle element 11 of an array is added to the sum of signals from summers 17 and 18 to form a sum pattern output. The amplitude distribution in rectangular coordinates for the sum and difference patterns as a function of the beam angle a from a direction normal to an array are shown in FIG. 6. For each array, there are pattern output signals from the respective pattern forming networks similar to what has been described for array 3. The sum pattern from the pattern fonning network 16 of array 3 and the pattern forming network 20 of array 1 are added together in adder 21 and are applied to the IF amplifier 22 to give a reference signal. The difference pattern of pattern forming network 16 is added to the difference pattern from the pattern forming network 20 and combined in adder 23. The output of adder 23 is applied to IF amplifier 24 and then to a synchronous detector 25 where the addition of two difference pattern signals from amplifier 24 is compared with the additive sum pattern signal from IF amplifier 22. The output of synchronous detector 25 is a direct current voltage which is applied to the repeller of klystron local oscillator 13 having a :18 mc. electronic tuning range to change the frequency of the klystron local oscillator signal thereby changing the phasing along the various output taps 15 along the RF delay line 14 for each array 1 and 3. The changing of the phasing of the outputs from the delay line 14 in both array 1 and 3 will move the receiving beam in the pitch plane to an angle directed at the target. When the receiving beam in the pitch plane is directed at the target, the direct current voltage E from the synchronous detector 25 is proportional to the phase difference between the output taps along the delay line and the phase difference between the received signals on the antenna elements 10. Since the phase difference t from Equation 2 is proportional to sin a, voltage E from detector 25 is proportional to sin where 4a is the pitch angle.

To determine the yaw angle of the target from the missile, the sum pattern outputs from'array 1 and array 3 are subtracted in adder 26, the output thereof fed to intermediate frequency amplifier 27 and then connected to synchronous detector 28, wherein the amplified signal from amplifier -27 is synchronously detected with the reference signal from amplifier 22. The direct current output signal from detector 28 is an indication of the phase dilference [between the signals received on array 1 and array 3. By reference to the analysis derived from FIG. 4, it will be evident that for array 1 and array 3 angle 11 becomes the yaw angle 0 and consequently the direct current voltage from the detector 28 is a measure of the phase difference p.

The voltage from synchronous detector 28 representing the phase difference between the received signals on array 1 and array 3 is connected to the continuous phase shifter 29. The phase shifter 29 changes the phase of the local oscillator frequency signal applied to the delay line 14 (for array 1 to shift the phase of the signals from the output taps of the delay line the same amount in order that the mixing of the local oscillator signal with the received signal will be maximized so that the sum pattern output obtained from the pattern forming network of each array are in phase. The amount of the phase shift fed to delay line 14 for array 1 is proportional to a coordinate, sin 6 of the bearing angle or lead angle to the target in the yaw plane.

The direct current voltage from detector 28 varies depending on the changing relationship between the missile and the target and is applied to a differentiating circuit 30. From the analysis of FIG. 4, as to the received signals between two spaced arrays, the voltage E from the dilfere-ntia-ting circuit 30 represents the differential of phase difference p that is 1). Since from equation (4), p is proportional to sin u, then 13 is proportional to it cos 1:. Voltage E derived from the received signals on arrays 1 and 3 consequently is proportional to cos 0 where 9 is the yaw angle from the missile to the target. The voltage E contains information indicative of the rate of change of yaw angle which is necessary for proportional navigation for control of the missile in the yaw plane thereof. However, voltage E contain-s the factor cos 6 which for large lead angles is not constant and represents an error in the measurement which can result in instability of the missile control system.

Similar circuits, not shown, are used for the detection of signals received on each of arrays 2 and 4. Since the axes of arrays 2 and 4 are normal to the axes of arrays 1 and 3, the receiving beam is scanned electronically in the yaw plane by changing the phasing of the output taps of a delay line. Similarly to the receiving channel for arrays 1 and 3, the received signals at arrays 2 and 4 are compared in phase to give a fine measure of the pitch angle. Accordingly, from arrays 2 and 4, the circuits measure and detect voltage E proportional to sin 0 and a voltage E proportional to 1) cos where 4: is the differential of the pitch angle.

For missile proportional navigation, 9 and are the desired quantities, but the voltages E and E include as a factor the cosine of the respective angles which has to be compensated for in applying control signals to operate the missile control surfaces, the corrections, cos 6 and cos p compensations, become extremely important for large lead angles such as encountered in high speed targets. The cos 0 and cos corrections for large lead angles will vary and result in instability of the missile control system. With the measurement by the present electronically scanned receiver having four antenna arrays of the sine of the pitch and yaw angles, the indication of rate of change of pitch and yaw angles can be determined without the necessity of accounting for the cosine corrections. The outputs E E E and E of the receiver channels are fed to computers 31 and 32 as indicated in FIG. 1 wherein voltages E and E are determined arrocrding to the following response E1 uT-rarf and The resulting voltages E and B are fed to the control system to effect proportional navigation of the missile to the target.

The present invention of an electronically steerable interferometer seeker results in increased receiving area and therefore an increase in received signal strength with greater accuracy and range detection of a target. With the multiple antenna arrays, angular resolution is improved to aiford better performance in the presence of clutter, multiple targets, and noise jamming. The seeker provides a direct maesure of target lead or bearing angle in the pitch and yaw planes to furnish a correction for the variation of angular rate sensitivity with the target position.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. An electronically scanned fan beam interferometer seeker for a semi-active terminal guidance system for determining lead angle and rate of change of lead angle of a target from a missile in the pitch and yaw planes of the missile comprising (a) four linear antenna arrays positioned on the periphery of the outer shell of the forward part of a missile, said four antenna arrays being positioned into two pairs of diametrically spaced arrays with the axes of said arrays in the same direction in each pair of arrays, one pair of arrays having a receiving fan beam scanning in the pitch plane of the missile, the other pair of arrays having a receiving fan beam scanning in the yaw plane of the missile, each of said arrays having seven equally spaced apart antenna elements,

(b) a balanced crystal mixer connected to each element of said arrays,

(c) a delay line for each antenna array having equally spaced apart output taps connected respectively to each mixer,

(d) a klystron local oscillator for each pair of diametrically spaced antenna arrays and connected to each of said delay lines of said pairs of arrays for supplying a local oscillator signal to said delay lines whereby a direct current voltage applied to the repeller of said klystron will vary the frequency of said local oscillator signal being fed to said delay lines which changes the amount of phasing of the output signals from the output taps of said delay line to match in each of said mixers the phasing between the received signals on said elements of an antenna array to produce an intermediate frequency signal,

(e) a pattern forming network for each linear array, said mixers of each array being connected to said pattern forming network and applying said intermediate frequency signal thereto, said pattern forming network for each array developing a sum pattern of said intermediate frequency signals and a difference pattern of said intermediate frequency signals from opposite sides of each array,

(f) a first adder connected to said network of each pair of arrays for adding the sum pattern of each of said pair of networks for forming a reference signal,

(g) a second adder connected to said network of each pair of arrays for adding the difference pattern of each of said pair of networks forming an additive difierence pattern signal,

(h) a third adder connected to said network of each pair of arrays for subtracting the sum pattern of each of said pair of networks for forming a difierence sum pattern signal,

(i) a first synchronous detector connected to said first and second adders for comparing said additive difference pattern signal with said reference signal establishing a direct current voltage proportional to a coordinate of the lead angle of the target in the pitch and yaw planes of said missile, said direct current voltage from said first detector being applied to the repeller of said klystron local oscillator whereby the amount of phasing of the output signal changes to mix with the received signals to scan the receiving beam in the pitch and yaw planes of the missile,

(J) a continuous phase shifter for each pair of arrays connected between said local oscillator and one of said delay lines,

(k) a second synchronous detector connected to said first and third adders for comparing said difference sum pattern signal with said reference signal for producing a second direct current voltage proportional to the phase difference between the received signals between the linear arrays of each pair of arrays, and being a measure of another coordinate of the lead angle of the target in the yaw and pitch planes of the missile, said second direct current voltage being applied to said continuous phase shifter to maintain the sum pattern from each of said pair of networks in each pair of arrays in phase,

(1) a pair of computers, said direct current voltage of said detectors being applied to said computers for establishing signals proportional to the true rate of change of the lead angle of the target in the yaw and pitch planes of the missile for effecting an accurate terminal guidance of the missile to the target.

2. An electronically scanned fan beam interferometer homing system for a semi-active terminal guidance system for determining the lead angle and rate of change of lead angle of a target from a missile in the pitch and yaw planes of the missile comprising (a) four linear antenna arrays positioned on the periphery of the outer shell of the forward part of a missile, said four antenna arrays being arranged into two pairs of diametrically spaced arrays with the axes of said arrays in the same direction in each pair of arrays, one pair of arrays having a receiving fan beam scanning in the pitch plane of the missile, the other pair of arrays having a receiving fan beam scanning in the yaw plane of the missile, each of said arrays having seven equally spaced apart antenna elements,

(b) a first receiving channel for said one pair of arrays, and a second receiving channel for said other pair of arrays, each of said channels having (1) balanced crystal mixers connected to each element of said pair of arrays respectively,

(2) two delay lines, each delay line for an antenna array of said pair of arrays, each of said delay lines having equally spaced apart output taps connected respectively to each mixer associated with an antenna array,

(3) a continuous phase shifter connected to one of said delay lines,

(4) a klystron local oscillator connected to said continuous phase shifter and the other of said delay line for supplying a local oscillator signal to said delay lines whereby the change in frequency of said local oscillator signal from the center frequency of said local oscillator signal determines the amount of progressive phase difference of the output signals from the output taps of said delay line for matching in each of said mixers the phase difference between the received signals on said elements of an array in order to produce an intermediate frequency signal from each of said mixers, I

(5) a pair of pattern forming networks, said mixers of each array being connected to one of said pattern forming networks, said intermediate frequency signal of said mixer being applied to each of said pattern forming networks for developing a sum pattern of said intermediate frequency signals and a difference pattern of said intermediate frequency signals from opposite sides of each array,

(6) a first adder connected to said pair of networks for adding a sum pattern of each of said pair of networks for forming a reference signal,

(7) a second adder connected to said pair of networks for adding the difference pattern in each of said pair of networks forming an additive difference pattern signal,

(8) a third adder connected to said pair of networks of each channel for subtracting the sum pattern of each of said pair of networks for forming a difference sum pattern signal,

(9) a first synchronous detector, said first and second adders connected to said first synchronous detector for comparing said additive difference pattern signal with said reference signal establishing a direct current voltage proportional to a coordinate of the lead angle of the target in the pitch and yaw planes of said missile respectively, said direct current voltage from said first detector being applied to said klystron local oscillator to change the frequency thereof whereby the 8, phase difference of the output signals of said delay lines change and mix with said received signals to scan the receiving beams in the pitch and yaw planes of the missile,

(10) a second synchronous detector connected to said first and third adders for comparing said difference sum pattern signal with said reference signal for producing a second direct current voltage proportional to the phase difference between the received signals between linear arrays of each pair of arrays, said second direct current voltage being applied to said continuous phase shifter to maintain the sum pattern from each of said pair of networks in phase, said second direct current voltage being a measure of a coordinate of a lead angle of the target in the yaw and pitch planes of the missile respectively,

(11) a differentiating circuit connected to said second detector for indicating a differential voltage signal proportional to the changes in the phase difference between the received signals on the linear arrays of each pair of arrays of each channel,

(c) a first computer, said first detector of said first channel and said differentiating circiut of said second channel being connected to said first computer for establishing a control signal proportional to the true rate of change of the lead angle of the target in the pitch plane of the missile,

(d) a second computer, said second detector of said second channel and said differentiating circuit of said first channel being connected to said second computer for establishing a control signal proportional to the true rate of change of the lead angle of the target in the yaw plane of the missile whereby the control signals effect an accurate terminal guidance of the missile to the target.

3. An electronically scanned fan beam interferometer homing system for a semi-active terminal guidance system for establishing proportional navigational signals for controlling a missile to a target comprising,

(a) a plurality of receiving antenna arrays positioned on the periphery of the outer shell of the forward part of a missile, each of said arrays having equally spaced apart antenna elements for receiving reflected target signals,

(b) mixing means connected to each element of said arrays,

(c) a delay line for each antenna array having equally spaced apart output taps connected respectively to each of said mixing means for applying a series of local oscillator signals to said mixing means respectively,

(d) means for supplying a variable local oscillator signal to said delay line whereby the variation of the frequency of said local oscillator signal changes the phase difference between the said series of local oscillator signals from said delay line, said mixing means producing an intermediate frequency signal being the difference between the local oscillator signal from said delay line and the received signal on said antenna element,

(e) electronic network means connected to said mixing means of each antenna array for summing together intermediate frequency signals from each of said mixing means forming a sum pattern signal and for summing the difference frequency signals between the mixing means associated with one side of an antenna array from the difference frequency signals between the mixing means associated with the other side of an antenna array forming a difference pat tern signal,

(f) electronic summing means connected to each of said network means for adding said sum pattern signals to form a reference signal and subtracting said sum pattern signals to form a difference pattern signal,

(g) synchronous detecting means connected to said summing means for comparing said added difference pattern signals with said reference signal establishing a direct current voltage proportional to a coordinate of the lead angle from the missile to a target, said direct current voltage being applied to the supplying means for changing the frequency of said local oscillator signal; and for comparing said subtracted sum pattern signal with said reference signal for producing a second direct current voltage proportional to the phase diiference between the received signals between said linear arrays being a measure of another coordinate of lead angle from the missile to the target, said second direct current voltage being applied to a continuous phase shifter of one array to maintain the sum pattern signals from said network means in phase,

(h) computing means connected to said synchronous detecting means for operating on said direct current voltages of said detecting means for producing an output signal proportional to the true rate of change of the lead angle from the missile to a target for effecting an accurate terminal guidance of the missile to the target.

4. An interferometer seeker comprising (a) linear antenna array means having equally spaced apart antenna elements for receiving target signals,

(b) mixing means connected to each of said elements,

(c) phase shifting and variable local oscillator means connected to said mixing means for supplying a series of local oscillator signals with progressively increasing phase shifts to said mixing means of each of said elements respectively, said mixing means producing from said receiving target signals and said local oscillator signals intermediate frequency output signals,

(d) electronic network and summing means connected to said mixing means for forming from said intermediate frequency output signals a reference signal, an additive difierence signal, and a difference sum signal,

(e) synchronous detecting means connected to said network and summing means for comparing said additive difference signal with said reference signal establishing a first direct current voltage and comparing said dilference sum signal with said reference signal for establishing a second direct current voltage, said synchronous detecting means connected to said phase shifting and variable local oscillator means for applying said first and second direct current voltages to said phase shifter and said oscillator means respectively to change the phase shifts of said local oscillator signals to effect scanning of said linear array means and to maximize receiving target signals on said array means.

5. An interferometer seeker for establishing signals for controlling a missile to a target comprising,

(a) linear antenna array means positioned on the periphery of the outer shell of the forward part of a missile having equally spaced apart antenna elements for receiving target signals,

(b) mixing means connected to each of said elements,

(c) variable local oscillator means connected to said mixing means for supplying a series of local oscillator signals to said mixing means of each of said elements respectively, said mixing means having intermediate frequency output signals being the difference between said receiving signals and said local oscillator signals,

(d) electronic network and summing means connected to said mixing means for forming from said intermediate frequency output signals a reference signal,

an additive ditference signal, and a difference sum signal,

(e) synchronous detecting means connected to said network and summing means for comparing said additive diiference signal with said reference signal and said difference sum signal with said reference signal for establishing direct current output signals proportional to the coordinates of the lead angle from the missile to a target for effecting control of the missile to a target.

6. An electronically scanned fan beam interferometer seeker for a semi-active terminal guidance system for determining the lead angle and rate of change of lead angle from a target to a missile comprising (a) two pairs of spaced apart linear antenna arrays, the axes of one pair of arrays being normal to the axes of the other pair of arrays, each linear array having a fan beam receiving pattern, each of said arrays having a plurality of equally spaced apart antenna elements,

(b) receiving channel means for each pair of arrays for operating on received signals on the arrays for determining a coordinate of the beam angle in the scan plane of an array of the signals from a target and for determining the phase difference between received signals in the fan beam plane of a pair of arrays indicating a coordinate of the lead angle to the target, said receiving channel means establishing direct current Voltages indicative of two coordinates of a beam angle of one pair of arrays and two coordinates of a beam angle of another pair of arrays for supplying to a missile control system an indication of the lead angle to a target,

(0) computer means connected to said receiving channel means for producing from said direct current voltages of said receiving channel means an output voltage for a missile control system indicative of the rate of change of lead angle to a target for effecting proportional navigational control of a missile to a target.

7. In an electronically scanned fan beam interferometer seeker for a semi-active terminal guidance system for determining the lead angle and rate of change of lead angle of a target from a missile having a pair of linear antenna arrays with each of said arrays having equally spaced apart antenna elements, and a receiving channel for said pair of arrays comprising (a) balanced crystal mixers connected to each element of said pair of arrays respectively,

(b) two delay lines, each delay line for an antenna array of said pair of arrays, each of said delay lines having equally spaced apart output taps connected respectively to each mixer associated with an antenna array (c) a continuous phase shifter connected to one of said delay lines.

(d) a klystron local oscillator connected to said continuous phase shifter and the other of said delay lines for supplying a local oscillator signal to said delay lines whereby the change of frequency of said local oscillator signal from the center frequency of said local oscillator signal determines the amount of progressive phase difference of the output signals from the output taps of said delay line for matching in each of said mixers the phase difference between the received signals on said elements of an array in order to produce an intermediate frequency signal from each of said mixers,

(e) a pair of pattern forming networks, said mixers of each array being connected to one of said pattern forming networks, said intermediate frequency signal of said mixer being applied to each of said pattern forming networks for developing a sum pattern of said intermediate frequency signals and a difference 11 pattern of said intermediate frequency signals from opposite sides of each array,

(f) a first adder connected to said pair of networks for adding a sum pattern of each of said pair of networks for forming a reference signal,

(g) a second adder connected to said pair of networks for adding the difference pattern in each of said pair of networks forming an additive difference pattern signal,

(h) a third adder connected to said pair of networks of each channel for subtracting the sum pattern of each of said pair of networks for forming a difference sum pattern signal,

(i) a first synchronous detector, said first and second adders connected to said first synchronous detector for comparing said additive difierence pattern signal with said reference signal establishing a direct current voltage proportional to a coordinate of the lead angle of the target, said direct current voltage from said first detector being applied to said klystron local oscillator to change the frequency thereof whereby the phase difference of the output signals of said delay lines change and mix with said received signals to scan the receiving beam,

(j) a second synchronous detector connected to said first and third adders for comparing said difierence sum pattern signal with said reference signal for producing a second direct current voltage proportional to the phase difierencebetween the received signals on said pair of arrays, said second direct current voltage being applied to said continuous phase shifter to maintain said sum pattern from each of said pair of networks in phase, said second direct current voltage being a measure of a coordinate of the lead angle to the target from the missile,

(k) a difierentiating circuit connected to said second detector for indicating a differential voltage signal proportional to the changes in the phase ditference between received signals on said pair of arrays,

(l) first computing means connected to said first detector and second computer means connected to said differentiating circuit for operating on said first direct current voltage and said differential voltage signal respectively for producing an output signal for a missile control system proportional to the true rate of change of the lead angle from the missile to a target for effecting accurate terminal guidance of the missile to the target.

No references cited.

25 CHESTER L. JUSTUS, Primary Examiner. 

5. AN INTERFEROMETER SEEKER FOR ESCABLISHING SIGNALS FOR CONTROLLING A MISSILE TO A TARGET COMPRISING, (A) LINEAR ANTENNA ARRAY MEANS POSITIONED ON THE PRERIPHERY OF THE OUTER SHELL OF THE FORWARD PART OF A MISSILE HAVING EQUALLY SPACED APART ANTENNA ELEMENTS FOR RECEIVING TARGET SIGNALS, (B) MIXING MEANS CONNECTED TO EACH OF SAID ELEMENTS, (C) VARIABLE LOCAL OSCILLATOR MEANS CONNECTED TO SAID MIXING MEANS FOR SUPPLYING A SERIES OF LOCAL OSCILLATOR SIGNALS TO SAID MIXING MEANS OF EACH OF SAID ELEMENTS RESPECTIVELY, SAID MIXING MEANS HAVING INTERMEDIATE FREQUENCY OUTPUT SIGNALS BEING THE DIFFERENCE BETWEEN SAID RECEIVING SIGNALS AND SAID LOCAL OSCILLATOR SIGNALS, (D) ELECTRONIC NETWORK AND SUMMING MEANS CONNECTED TO SAID MIXING MEANS FOR FORMING FROM SAID INTERMEDIATE FREQUENCY OUTPUT SIGNALS A REFERENCE SIGNAL, AN ADDITIVE DIFFERENCE SIGNAL, AND A DIFFERENCE SUM SIGNAL, (E) SYNCHRONOUS DETECTING MEANS CONNECTED TO SAID NETWORK AND SUMMING MEANS FOR COMPARING SAID ADDITIVE DIFFERENCE SIGNAL WITH SAID REFERENCE SIGNAL AND SAID DIFFERENCE SUM SIGNAL WITH SAID REFERENCE SIGNAL FOR ESTABLISHING DIRECT CURRENT OUTPUT SIGNALS PROPORTIONAL TO THE COORDINATES OF THE LEAD ANGLE FROM THE MISSILE TO A TARGET FOR EFFECTING CONTROL OF THE MISSILE TO A TARGET. 